The overall objective of the proposed research is the diagnostic detection and differentiation of specific types of myocardial pathology in vivo noninvasively based on ultrasonic characterization of the tissue itself, as opposed to assessment of dimensions or motion. The underlying hypothesis is that pathologic changes occuring in myocardium alter the physical properties of the tissue, and that these alterations can be quantified with indexes based on the frequency dependences of the ultrasonic attenuation and backscatter. Much of the work focuses on ischemic injury because of the need to detect it definitively and quantify its progression, and in part because of the need to detect it definitively and quantify its progression, and in part because of the wealth of information available regarding its structural concomitants Studies will be performed to: (1) employ ultrasonic tissue characterization in order to delineate the frequency dependence of the attenuation coefficient based on analysis of reflected (rather than transmitted) ultrasound, making feasible its future clinical application; (2) determine quantitative values of backscatter and attenuation in the presence of intervening chest wall; (3) delineate specific structural components of myocardium and determinants of ultrasonic attenuation and backscatter such as myosin content, presence of aggregates of calcium accumulated during myocardial injury, and the phasic status of the contractile apparatus in vitro and in vivo; and (4) define the quantitative ultrasonic properties of intracavitary thrombus during its evolution to provide a basis of its recognition in patients. Results of these investigations should broaden the diagnostic and quantitative power of ultrasound by permitting noninvasive detection and quantification of myocardial injury in patients based on characterization of cardiac tissue.